1. Field of the Invention
The present invention relates to a rod integrator holder that holds a rod integrator disposed on an optical path to homogenize the luminous flux density within a plane perpendicular to the optical axis in an illumination optical system or the like of a projection type image display apparatus, and to a projection type image display apparatus having the same.
2. Description of the Prior Art
In illumination optical systems of projection type image display apparatuses such as video projectors in which illumination light is optically modulated by an image display device such as a digital micromirror device (hereinafter referred to as “DMD”) and the thus modulated light is projected under magnification, optical prisms known as rod integrators have conventionally been used as means for homogenizing the luminous flux density in order to illuminate the image display device uniformly. The rod integrators have been configured such that an incident luminous flux is repeatedly totally reflected therewithin and then is emitted therefrom while the luminous flux density distribution within a plane perpendicular to the optical axis becomes substantially uniform. In particular, within an illumination optical system, a rod integrator is often disposed downstream of a color wheel apparatus acting as color decomposing means.
As a holding structure for holding this kind of rod integrator within an illumination optical system, various types have conventionally been known (see Patent Documents 1 to 3 shown below). In these holding structures, since the light exit face of the rod integrator is exposed, the following problem arises:
Since the light exit face of the rod integrator is exposed, the light exit face can be damaged and dust or the like can attach to the light exit face. An illumination optical system using a rod integrator is configured such that the light exit face of the rod integrator and the device surface of an image display device have an optically conjugate relationship therebetween. Therefore, if the light exit face of the rod integrator is damaged or dust or the like attaches thereto, an image of dust or the like will be formed on the device surface of the image display device. The image of damage, dust, or the like formed on the device surface is superposed on an image displayed by the image display device, and is projected onto a screen under magnification.
In view of the foregoing circumstances, the inventor of the present application has proposed a rod integrator holder capable of holding a rod integrator while the light exit face thereof is tightly closed (see Patent Document 4 shown below). This rod integrator holder comprises: a tubular case for inserting and holding the rod integrator; and a brim-like wall provided at one end part of the case. By allowing the brim-like wall to abut against one end part of the lens barrel, the space between the lens barrel and the case is tightly closed.
[Patent Document 1]
Japanese Unexamined Patent Publication No. H08-227034
[Patent Document 2]
Japanese Unexamined Patent Publication No. H11-326727
[Patent Document 3]
Japanese Unexamined Patent Publication No. 2002-131840
[Patent Document 4]
Japanese Unexamined Patent Publication No. 2003-232974
When the rod integrator is held by being inserted in a tubular case, in order that the side faces of the rod integrator and the inner faces of the case are not in contact with each other, a predetermined gap is interposed therebetween. It is desirable that this gap be as small as possible. When this gap is large, the possibility increases that part of the light from the light source section passes through the gap and the shape of the gap is projected onto the screen through the image display device.
However, when this gap is small, the following problem arises: The rod integrator is held within the case through a plate spring, an adhesive or the like, and when the gap is small, it is more likely that the edges of the rod integrator in the direction of the length (the direction of the optical axis) come into contact with the inner faces of the case when some vibration is applied. Since the edges of the rod integrator are weak in strength, when they come into contact with the inner faces of the case, there are possibilities where they are broken and desired optical performance cannot be obtained and that the edges of the rod integrator and the inner faces of the case rub against each other to generate dust due to abrasion. When dust due to abrasion is caused, the dust attaches to the light exit face of the rod integrator and is projected onto the screen under magnification as mentioned above.